Recently, research and development regarding a human type robot which acts in a human's living environment, a so-called humanoid robot, have been widely carried out. The humanoid robot is often used for the purpose of making human life such as not only industrial production but also housework, nursing care for the elderly, etc., comfortable, and must work bearing closely near many and unspecified users in environments made for humans. Therefore, it is requested for the humanoid robot to have the form and performance adapted to the works. Further, the humanoid robot is requested to provide a safe and flexible interface without specific use training, and there are an extremely large number of research subjects. In particular, bipedal walking robots, which have two legs similar to a human as moving means and perform bipedal walking, have been diligently researched and developed in many research institutes and enterprises.
A serial link mechanism with low kinematic constraint has been employed as a leg mechanism common to conventional bipedal walking robots. The serial link mechanism is a mechanism which serially connects a plurality of links, and has been widely used for an industrial manipulator, etc.
As a bipedal walking robot whose legs are constituted by such a serial link mechanism, “a bipedal walking robot comprising: a base body; one or more link mechanism(s) having one or more joint(s) which is/are connected to the base body and connects two links; driving means for driving the joint(s) of the link mechanism(s); and a control unit which controls operation of the driving means” is disclosed in Japanese Published Unexamined Patent Application No. 5-237775 (referred to as Patent reference 1 hereinafter).
FIG. 7 is a schematic view of the conventional bipedal walking robot. Moreover, in FIG. 7, an explanation regarding only a right leg will be provided and an explanation of a left leg will be omitted, as the constitution of the left leg is similar to the constitution of the right leg.
In FIG. 7, reference numeral 100 denotes a conventional bipedal walking robot, 101 denotes a joint for a rotational movement of a crotch, 102 denotes a joint for a longitudinal movement of the crotch, 103 denotes a joint for a lateral movement of the crotch, 104 denotes a joint for a longitudinal movement of a knee, 105 denotes a joint for a longitudinal movement of an ankle, 106 denotes a joint for a lateral movement of the ankle, 107 denotes a foot, 108 denotes a base body, 109 denotes a thigh link connecting the joints of the crotch 101, 102 and 103 with the joint of the knee 104, and 110 denotes a lower thigh link connecting the joint of knee 104 with the joints of the ankle 105 and 106.
As shown in FIG. 7, the conventional bipedal walking robot 100 includes the respective six joints in the right leg and left leg. The crotch and ankle are respectively provided with the joint for longitudinal movement and the joint for lateral movement so that the two joints squarely intersect, axis lines of the joints intersect at one point of space. It is constituted in such a way that rotating axes of the joint for longitudinal movement of the crotch 102, the joint for longitudinal movement of the knee 104 and the joint for longitudinal movement of the ankle 105 are arranged in parallel with each other, the relative positional relationship between the three joints 102, 104 and 105 is not changed regardless of the other three degrees of freedom of movement. Further, the joint for rotational movement 101 is provided in the crotch as a third degree of freedom which makes the whole leg rotate, a rotating axis of the joint 101 is provided so as to be made orthogonal to each axis of the joints 102 and 103 at an intersection of the joints 102 and 103.
Further, “a parallel link for robot driving mechanism which relatively drives a first member and a second member with space of six degrees of freedom, wherein: the parallel link mechanism is constituted by three or more unit links which respectively connect the first member with the second member and have a driving function with two degrees of freedom; and each unit link includes a first arm and a second arm, a rotating driving joint with one degree of freedom which connects the first member with the first arm, a rotating driving with one degree of freedom rotating follower joint with one degree of freedom which connects the first arm with the second arm and a rotating follower joint with three degrees of freedom which connects the second arm with the second member” is disclosed in Japanese Published Unexamined Patent Application No. 2001-121460 (referred to as Patent reference 2 hereinafter).
However, in the above-described conventional arts, there remain problems as follows.    (1) The bipedal walking robot disclosed in the Patent reference 1 cannot structurally sustain a large load, because the legs thereof are constituted by the serial link mechanisms and therefore output power of feet provided on the tip of the legs is small. For example, a heavy load as an upper half body cannot be mounted or incorporated, and therefore the degree of freedom in designing is deficient, or when arms, etc., are provided on the upper half body, it is impossible to move with a heavy load in arms at high speed, and therefore a problem resides in the fact that practicality is lacking.    (2) Further, the conventional bipedal walking robot is designed so as to cooperatively operate by combining the upper half body with the lower half body, because the legs of the lower half body thereof structurally lack stability owing to the constitution by the serial link mechanisms. Thus, since it is difficult to design only a lower half body, it is requested that the lower half body is designed considering the structure of an upper half body, and consequently a problem resides in the fact that the degree of freedom in designing is deficient.    (3) In the parallel link for the robot driving mechanism disclosed in the Patent reference 2, each unit link is constituted by the first and second arms serially connected with each other. Thus, when the parallel link for robot driving mechanisms are employed in the left and right legs of the robot, the mechanisms interfere with each other and operations are offset, and consequently a problem resides in the fact that both the degree of freedom in designing and practicality are deficient.
In order to solve the above conventional problems, the present invention was made, and
it is an object of the present invention to provide a lower half body module of a bipedal walking robot which is excellent in practicality in the point that it is possible to transport a heavy load, and which is excellent in the degree of freedom in designing in the point that it is possible to mount or incorporate an upper half body having a large weight. Therefore, this is why legs of the lower half body module are constituted by a parallel link mechanism to sustain a large load.